The present invention relates to an arrangement in a hybrid electric vehicle (HEV) equipped with a combustion engine, a transmission and at least one electric motor/generator, and where a power electronics unit of the electric motor/generator is mounted on a gearbox of said transmission.
The need to reduce fossil fuel consumption and emissions in vehicles powered by an internal combustion engine (ICE) is well known. Vehicles powered by electric motors attempt to address these needs. However, electric vehicles have limited range and limited power capabilities and need substantial time to recharge their batteries. An alternative solution is to combine both an ICE and electric traction motor into one vehicle. Such vehicles are typically called Hybrid Electric Vehicles (HEVs). See for example, U.S. Pat. No. 5,343,970.
The HEV is described in a variety of configurations. Many HEV patents disclose systems in which an operator is required to select between electric and internal combustion operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.
Other, more useful, configurations have developed. For example, a Series Hybrid Electric Vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels.
A Parallel Hybrid Electrical Vehicle (PHEV) configuration has an engine (most typically an ICE) and an electric motor that together provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE. The PHEV has usually a transmission between the ICE and drive wheels of the vehicle in order to be able to alter gear ratio between the ICE and the drive wheels and also in many cases between the electric motor and the drive wheels.
A Parallel/Series Hybrid Electric Vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is typically known as a “powersplit” configuration. In the PSHEV, the ICE is mechanically coupled to two electric motors in a planetary gearset transaxle. A first electric motor, the generator, is connected to a sun gear. The ICE is connected to a carrier. A second electric motor, a traction motor, is connected to a ring gear (output) via additional gearing in a transaxle. Engine torque powers the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery if a regenerative braking system is used.
The desirability of combining an ICE with an electric motor is clear. The ICE's fuel consumption and emissions are reduced with no appreciable loss of vehicle performance or range. Nevertheless, there remains a substantial opportunity to develop ways to optimize HEV operation.
One area of development is maintaining the desired operating temperature of the HEV components. A cooling system maintains optimal component operation and performance. Overheated components adversely affect efficiency and may eventually cause component failure.
A typical prior art cooling arrangement for an ICE vehicle has a coolant fluid in an enclosed loop that passes through certain vehicle components and a heat exchanger (radiator). A heater core is also typically added to vent engine heat into the passenger compartment as desired. The engine and transmission components typically require cooling from a liquid cooling system. As the coolant circulates through these components in the closed loop, it absorbs heat that is released as the coolant passes through the radiator and heater core.
Coolant flow in the prior art cooling arrangement is typically controlled by a pump driven front-end accessory drive (FEAD). As engine speed increases, the speed of the pump also increases allowing more coolant flow through the system. Additionally, a thermostat within the loop only allows coolant flow through the radiator after the coolant temperature reaches a level at which the engine temperature has stabilized and is considered “warmed up.”
Though simple and reliable, the prior art coolant control system comprising a pump and a thermostat is inadequate for HEVs. For example, the HEV has additional components that require cooling, such as a power electronics unit. Further, the prior art coolant pump does not function when the engine is off. Thus, the typical vehicle accessories driven by the FEAD (including the coolant pump, air conditioning, and power steering) in a conventional vehicle must be powered by an alternate source in the HEV to maintain their functionality when the engine is not running.
The cooling arrangement of a prior art transmission usually comprises a predetermined amount of cooling lubricant contained in the transmission housing. Some of the gear wheels of the transmission are arranged to be in contact with the cooling lubricant. When the gear wheels of the transmission rotate during operation, the cooling lubricant is splashed around in the transmission housing, making the lubricant coming into contact with basically all parts inside the transmission housing. The lubricant evens the heat build up in the transmission and contributes to heat being conducted to the transmission housing. The transmission housing can be cooled by ambient air. There are also transmission cooling arrangements where the lubricant is circulated by a pump through cooling channels inside the transmission housing and outside the transmission housing to a heat exchanger.
In a heavy HEV, such as a truck more than 5 tonnes it is common for an electric motor/generator to have a performance capacity of more than 100 kW. A power electronics unit for such a relatively powerful electric motor/generator produces a lot of heat during operation that has to be cooled in order to secure the endurance of the electronic components in the power electronics unit. Depending on the specification of the electronic components the maximum allowable temperature varies. Electronic components with less heat resistance are cheap and can have a maximum operative temperature of, for example, 60 degrees Celsius. If the electronic components are specified to withstand temperatures of several hundred degrees Celsius then usually less cooling of the power electronics unit is needed. On the other hand such electronic components are expensive. In the future the power electronics unit is expected to shrink in size due to technical development. The demand for cooling will probably increase since the electronic components will be more densely packed and the electric power handled by the power electronics unit will increase concurrently with the use of more powerful electric motor/generators used in future HEV.
US2004/0134695 discloses a vehicle power train with a combustion engine, a gearbox and an Integrated Starter/Generator (ISG) arranged between the combustion engine and the gearbox. Thus, this document does not disclose a HEV, still, in one embodiment disclosed the power electronics unit of the ISG is arranged on the gearbox. The power demand of an ISG is usually between 1 to 5 kW. The power electronics unit of the ISG is, thus, relatively small and handles a relatively low power. The need for cooling is relatively small. Further, this document discloses an embodiment where a cooling arrangement of the engine also is used for cooling the power electronics unit, when the power electronics unit is arranged on the engine. Only two standard mounting points for a conventional ring gear starter are used when the power electronics unit is mounted on the engine. There is also disclosed a plug in connection between the power electronics unit and the ISG.
Noise from a vehicle power train is always an issue. The transmission components of a vehicle transmission contributes to the increase of noise when in operation. A step geared transmission, especially when gear changing frequently, can cause slamming and rattling, which can be disturbing for the environment. A known noise damping solution is to arrange a relatively thin plate on the outside of the transmission housing. The fixing point of the plate extends around the whole periphery of one side of the plate. Said transmission outside, said plate side and said fixing point enclose a compartment comprising a medium, such as air, with high noise damping capabilities. The fixing point as such can be of a noise damping material such as rubber or the like.
It is desirable to make an arrangement for a power electronics unit in a HEV more space effective with a minimal amount of components. It is desirable to contribute to a simple and effective installation of a cooling arrangement of said power electronics unit and to contribute to noise reduction of said vehicle.
The arrangement according to an aspect of the invention is an arrangement for a power electronics unit in a hybrid vehicle power train, said hybrid vehicle power train comprising a combustion engine arranged for propulsion, and an electric motor/generator arranged for propulsion, a transmission with a transmission housing, said transmission is arranged to adapt gear ratio between at least one of said propulsion units and driven vehicle wheels. Said motor/generator is arranged to exchange electric power with a power electronics unit. A cooling arrangement is arrange for cooling at least said transmission with said transmission housing. Said power electronics unit is shaped substantially as a plate, where a first biggest cross-sectional area of said plate is extended substantially along and substantially within a first transmission side of said transmission housing and covering at least a part of said first transmission side, said power electronics unit is fixed to said hybrid vehicle power train with at least one first attachment point. The invention is characterized, according to an aspect thereof, in that all attachment points have a total thermal conductivity corresponding to less than 10 degrees temperature difference on a Kelvin-scale between electronics of said power electronics unit and the outside of said first transmission side for 5 kW of heat originating from one side of said attachment point.
The advantage is that in this way a cooling arrangement for said transmission (for example air cooling of transmission housing and transmission lubricant or cooling of transmission with cooling fluid flowing through cooling channels or cooling of transmission with channels leading transmission lubricant through a heat exchanger in a cooling system with cooling fluid) can be used for cooling said power electronics unit, especially during temporary peak loads. The opposite can also happen, that is, that a cooling arrangement for cooling said power electronics unit can be used to cool said transmission especially when the loads on the transmission are high. If there is no cooling arrangement with cooling channels the relatively big mass of the transmission will advantageously contribute to level out temporary heat peaks in the power electronics unit.
A further advantage with the arrangement according to an aspect of the invention is increased space efficiency of the power electronics unit installation at the same time as the thermal conductivity of the attachment point/-s has/have been increased, which increases the performance of the cooling arrangement of the power electronics unit.
According to one embodiment of the arrangement according to an aspect of the invention a first side of said power electronics unit, facing said transmission, and said first transmission side are in contact with each other, forming said first attachment point as a wall to wall attachment point.
According to one embodiment of the arrangement according to an aspect of the invention said first side of the power electronics unit and said first transmission side are integrated and form a common wall between said transmission and electronics of said power electronics unit. In this way less parts can be used and a better thermal conductivity is achieved.
According to one further embodiment of the arrangement according to an aspect of the invention said common wall comprises cooling channels connected to said cooling arrangement for cooling said power electronics unit and said transmission. Thus, the cooling channels are used for cooling both the transmission and the power electronics unit.
According to one further embodiment of the arrangement according to an aspect of the invention said electric motor/generator and said power electronics unit are connected and fixed to each other. Said connection is a second attachment point formed by a plug in connection. In a further developed embodiment said plug in connection is arranged to transmit at least one of or both of a cooling medium for said cooling arrangement and electric power between said motor/generator and said power electronics unit. The advantage is that the number of electric wires and/or cooling medium tubes can be decreased.
In a further embodiment of an aspect of the invention said power electronics unit plate is arranged to cover said first transmission side in such a way as to damp noise originating from said transmission. In a further developed embodiment this is achieved by said power electronics unit comprising a casing of noise damping material, and which casing covers said electronics when arranged on said first transmission side. The advantage is that the power electronics unit also can be used for damping noise. In a even further developed embodiment of the invention said power electronics unit plate comprises said noise damping design and in an extended part only of a noise damping material, and where said extended part is arranged in order to better cover said first transmission side.
According to one embodiment of the arrangement according to an aspect of the invention a second electric motor/generator with a second power electronics unit are arranged in connection to said transmission, and where said second power electronics unit is arranged along a second transmission side of said transmission housing. The advantage is that the number of components can be decreased further and the noise reduction capabilities can be kept on a high level without any additional noise reducing components.